Previous research has shown that vitamin D deficiency increases the risk of heart disease, heart attack and stroke, but the level of deficiency associated with such risk was unclear, the researchers said.

Having a vitamin D level anywhere above 15 nanograms per milliliter is fine for heart health, according to a team at the Intermountain Medical Center Heart Institute in Salt Lake City.

"Although vitamin D levels above 30 were traditionally considered to be normal, more recently, some researchers have proposed that anything above 15 was a safe level. But the numbers hadn't been backed up with research until now," lead researcher Dr. J. Brent Muhlestein, co-director of cardiovascular research, said in an institute news release.

"Even if any level above 15 is safe, one out of 10 people still have vitamin D levels lower than that. This equates to a very large percentage of our population. The best way to determine one's vitamin D level is by getting a blood test," he added.

The study, which included 230,000 people who were followed for three years, was presented this week at the American Heart Association's annual meeting, in Orlando, Fla. Research presented at meetings is typically viewed as preliminary until published in a peer-reviewed medical journal.

The body naturally produces vitamin D when exposed to the sun. The vitamin is also found in foods such as fish, fish liver oils, egg yolks, and some dairy and grain products. Vitamin D supplements are another option, the researchers said.

"This study sheds new light and direction on which patients might best benefit from taking vitamin D supplements," Muhlestein said.